A typical mobile communication system is shown in FIG. 8. A mobile communication system 400 includes mobile station devices (Mobile Station: hereinafter referred to as an MS) 410a and 410b connected to radio base station devices (hereinafter appropriately referred to as a NodeB) 420a and 420b, respectively, a radio access network 450 conforming to 3GPP (Third Generation Partnership Project), and a core network 480, as shown in FIG. 8. The “NodeB” is standardized as a logical node for wireless link for UE in a Cell.
The radio access network 450 comprises RNC (Radio Network Controller) 440a and 440b, and the NodeB 420a and 420b connected to the RNC 440a and 440b, respectively. The core network 480 includes an MSC (Mobile Switch Controller) 460 connected to the RNC 440a and 440b, and an HLR (Home Location Register) 470 connected to the MSC 460 (for example, refer to Non-Patent Document 1). Instead of the HLR, a VLR (Visitor Location Register) may be used.
The RNC 440a, 440b is a wireless controller. The NodeB 420a, 420b is a radio base station device. The MS 410a, 410b is a mobile station device. The MSC 460 is a mobile switch station. The HLR 470 is a subscriber information database.
Referring to FIG. 9, a communication procedure for the mobile communication system 400 configured in this way will be described below. In FIG. 9, the MS 410a existing in a wireless zone of the NodeB 420a is a communication source, and the MS 410b is a communication destination.
In FIG. 9, the MS 410a is connected via the NodeB 420a to the RNC 440a in starting the communication. Then, the MS 410a sends a call origination request to the RNC 440a (S401). The RNC 440a makes an inquiry of the MSC 460 about whether or not the communicating MS 410b is connectable (S402). The MSC 460 searches the HLR 470 and acquires the information on the MS 410b from the HLR 470 (S403).
The MSC 460 determines whether or not the RNC 440a is connectable to the communicating MS 410b via the NodeB 420b, RNC 440b and MSC 460 to which the MS 410b is connected, based on the acquired information about the MS 410b. If it is determined that the RNC 440a is connectable, the MSC 460 instructs the RNC 440a to connect to the MS 410b (S404). Also, the MSC 460 calls the MS 410b and receives a call response from the MS 410b (S405).
The RNC 440a, upon receiving an instruction, is firstly connected to the NodeB 420a (S406). Then, the MS 410a sends user data for the MS 410b to the NodeB 420a, and starts the communication (S407). Hence, a path C of the user data in the mobile communication system 400 is necessarily transmitted by way of the MSC 460, as shown in FIG. 10. That is, in the mobile communication system 400 as shown in FIG. 8, all the calls are processed through the MSC 460. Therefore, even if one mobile station of a communication destination and another communication source exist under the command of an identical radio base station device, the user data passed through a redundant path through the mobile switch station.
To shorten such a redundant path for the user data, there is a technique for extension transmission or reception of user data by providing an extension transmitting/receiving server in a radio access network 50 as shown in FIG. 11 (for example, refer to Patent Document 1). The technique for extension transmission or reception of user data will be described below.
A mobile communication system 100 includes the MS 10a and 10b, a radio access network 50, and a core network 80, as shown in FIG. 11. The radio access network 50 comprises the NodeB 20a, 20b, an extension transmitting/receiving server device 30, and the RNC 40a, 40b. The core network 80 includes an MSC 60 and an HLR 70.
The MS 10a and 10b are mobile station devices that perform wireless communication for transmitting or receiving data to or from the radio base station device by wireless. The MS 10a and 10b are connected to the NodeB 20a and 20b by wireless, respectively, and exist under the command of the NodeB 20a and 20b. In addition, the MS 10a and 10b, each transmits or receives the user data and control data to or from the NodeB 20a and 20b, respectively. Multiple MSs may be connected to one NodeB. Also, each MS 10a, 10b may perform both the transmission and reception of data, or either the transmission or reception of data. The radio access network 50 relays data between the core network 80 having the MSC 60 and the MS 10a, 10b. 
The radio access network 50 relays data between the core network 80 and the MS 10a, 10b, with the use of the NodeB 20a, 20b and the RNC 40a, 40b. 
The NodeB 20a and 20b are the radio base station devices that perform wireless communication for transmitting or receiving data to or from the MS 10a and 10b by wireless, respectively. The NodeB 20a and 20b are connected to the MS 10a and 10b by wireless, respectively. Also, the NodeB 20a and 20b are connected to the RNC 40a and 40b, respectively. Further, the NodeB 20a and 20b are connected to the extension transmitting/receiving server device 30. And the NodeB 20a and 20b, each transmits or receives the user data and control data to or from the MS 10a and 10b and the RNC 40a and 40b, respectively. The control data includes the mobile station control data transmitted or received between the MS 10a and 10b and the RNC 40a and 40b, and the control data regarding the extension transmission or reception (hereinafter referred to as the “extension transmission/reception control data”). Also, the NodeB 20a and 20b transmits or receives the user data to or from the extension transmitting/receiving server device 30. Multiple NodeBs may be connected to a single RNC. Also, Multiple extension transmitting/receiving servers may be connected to a single NodeB.
The extension transmitting/receiving server device 30 includes a NodeB interface 31, an RNC interface 32, a control signal processor 33, and a user data processor 34, as shown in FIG. 12. The NodeB interface 31 is a base station transmitting/receiving part for transmitting or receiving user data transmitted or received between MS 10a and MS 10b to or from the NodeB 20a and 20b by extension transmission or reception of data in the radio access network 50, respectively. The NodeB interface 31 transmits or receives the user data and extension transmission or reception control data to or from the NodeB 20a and NodeB 20b. The RNC interface 32 transmits or receives the extension transmission/reception control data to or from the RNCs 40a and 40b. 
The control signal processor 33 processes the extension transmission/reception control data transmitted or received by the NodeB interface 31 and the RNC interface 32. For example, the control signal processor 33 acquires the extension transmission/reception control data received by the RNC interface 32 from the RNC interface 32. The control signal processor 33 controls the user data processor 34 based on the acquired extension transmission/reception control data. For example, when acquiring a notification of transmitting or receiving user data transmitted or received between MS 10a and MS 10b by extension transmission or reception, the control signal processor 33 instructs the user data processor 34 to transmit the user data, received from the NodeB 20a connected to the MS 10a, in which the MS 10a is the communication source and the MS 10b is the communication destination to the NodeB 20b connected to the MS 10b. Also, the control signal processor 33 instructs the user data processor 34 to transmit the user data, received from the NodeB 20b connected to the MS 10b, in which the MS 10b is the communication source and the MS 10a is the communication destination to the NodeB 20a connected to the MS 10a. In this way, the control signal processor 33 instructs the user data processor 34 to transmit or receive the user data by extension transmission or reception. Also, the control signal processor 33 generates the extension transmission/reception control data, and inputs it into the NodeB interface 31 or the RNC interface 32.
The user data processor 34 controls the transmission or reception of the user data in the NodeB interface 31. The user data processor 34 instructs the NodeB interface 31 to transmit the user data received from the NodeB 20a and 20b respectively connected to the MS 10a and 10b of communication source, to the NodeB 20b and 20a connected to the communicating MS 10b and 10a under the control of the control signal processor 33. More specifically, the user data processor 34 acquires the user data received from the NodeB interface 31.
The user data processor 34 decapsulates the acquired user data, if the user data is encapsulated at the IP address of the extension transmitting/receiving server device 30. The user data processor 34 acquires the identification information of identifying the communication source and the communication destination of user data after decapsulation. Also, the user data processor 34 inputs the user data after decapsulation into the NodeB interface 31. If the transmission destination IP address of user data is translated into the IP address of the extension transmitting/receiving server device 30, the user data processor 34 acquires the IP address of the communicating MS from the user data and inversely translates the acquired transmission destination IP address of user data into the IP address of the communicating MS. The user data processor 34 acquires the identification information for identifying the communication source and the communication destination of user data after inverse translation. Also, the user data processor 34 inputs the user data after inverse translation into the NodeB interface 31.
The user data processor 34 determines which NodeB should transmit the received user data based on the acquired identification information of the communication source and the communication destination of the user data and the instruction from the control signal processor 33. Then, the user data processor 34 directs the NodeB for transmitting the user data to the NodeB interface 31, based on the determination result. The identification information includes the IP address of the MS 10a, 10b, the user ID of the user who uses the MS 10a, 10b, and the mobile station ID, for example.
Referring to FIG. 13, a communication procedure using the mobile communication system 100 with the above configuration will be described below. Firstly, the MS 10a sends a call origination request for transmission of the user data for the MS 10b to the MSC 60 via the NodeB 20a and the RNC 40a (S101). The MSC 60 acquires the identification information of the NodeB 20a, 20b, to which the MS 10a of communication source and the communicating MS 10b are connected, respectively, as the subscriber information from the position registration information, with reference to the HLR 70 (S102). Thereby, the MSC 60 detects that the MSs 10a and 10b is connected to the NodeB 20a and 20b, respectively.
The MSC 60 references the extension transmitting or receiving server connection information of the NodeB 20a, 20b, based on the identification information of the NodeB 20a, 20b. Thereby, the MSC 60 detects that the NodeB 20a to which the MS 10a is connected is connected to the extension transmitting/receiving server device 30, and that the NodeB 20b to which the MS 10b is connected is connected to the extension transmitting/receiving server device 30. The MSC 60 judges that the user data is transmitted or received by the extension transmission or reception, because the extension transmitting/receiving server device 30 connected to the NodeB 20a, 20b exists. Then, the MSC 60 selects the extension transmitting/receiving server device 30 as the extension transmitting/receiving server to be used for the extension transmission or reception (S103).
Next, the MSC 60 instructs the RNC 40b to call the MS 10b (S104). The RNC 40b calls the MS 10b upon receiving the instruction, and then the MS 10b responds to the call (S105). The RNC 40b notifies the MSC 60 that the response to the call is received (S106). The MSC 60, upon receiving the call response, notifies the extension transmitting/receiving server device 30 that the user data to be transmitted or received between MS 10a and MS 10b is transmitted or received by the extension transmission or reception (S107). Further, the MSC 60 notifies the transmission or reception to be performed by extension transmission or reception and the IP address of the extension transmitting/receiving server device 30 used for the extension transmission or reception, to the NodeB 20b to which the communicating MS 10b is connected and the NodeB 20a to which the MS 10a of the communication source is connected (S108, S109).
Through the above process, the communication starts between MS 10a and MS 10b (S110). After the start of the communication, the MS 10a of communication source transmits the user data to the NodeB 20a (S111). The NodeB 20a transmits the received user data to the extension transmitting/receiving server device 30 by translating the transmission destination IP address of the user data received from the MS 10a into the IP address of the extension transmitting/receiving server device 30, or encapsulating the received user data at the IP address of the extension transmitting/receiving server device 30 (S112). The extension transmitting/receiving server device 30 transmits the received user data directly to the NodeB 20b by means of the extension transmission or reception by inversely transforming the transmission destination IP address of the user data received from the NodeB 20a into the IP address of the communicating MS 10b, or decapsulating the received user data (S113). At step (S113), the user data is transmitted or received without being passed through the RNC 40a, RNC 40b or the MSC 60. The NodeB 20b transmits the received user data to the MS 10b (S114).
Hence, the path A of the user data in transmitting or receiving the user data by the extension transmission or reception in the mobile communication system 100 is shown in FIG. 14. The user data is transmitted or received over the path A from the MS 10a, NodeB 20a, the extension transmitting/receiving server device 30, NodeB 20b to MS 10b, without passing through the MSC 60. That is, the NodeB 20a of the communication source connected to the MS 10a of the communication source receives the user data transmitted from the MS 10a of the communication source and then transmits the user data to the extension transmitting/receiving server device 30, without passing through the MSC 60, the extension transmitting/receiving server device 30 receives the user data from the NodeB 20a of communication source, and then transmits the user data to the communicating NodeB 20b connected to the communicating MS 10b. The communicating NodeB 20b receives the user data from the extension transmitting/receiving server device 30, and then transmits the user data to the communicating MS 10b. Hence, the data transmitted from the MS 10a of the communication source arrives at the communicating MS 10b by way of the path A in the radio access network 50.
After the start of the communication at step (S110), the NodeB 20a, 20b transmits or receives the mobile station control data transmitted or received between MS 10a and MS 10b via the MSC 60. Hence, the mobile station control data transmitted or received between MS 10a and MS 10b is transmitted or received via the MSC 60. That is, the mobile station control data is transmitted or received over the path from the MS 10a, NodeB 20a, RNC 40a, MSC 60, RNC 40b, NodeB 20b to MS 10b. It should be noted that the user data is transmitted over the path without passing through the core network, whereas the mobile station control data is transmitted over the path via the core network.
With the above communication procedure, it is possible to transmit or receive the user data by means of the extension transmission or reception between the NodeB 20a, 20b and the extension transmitting/receiving server device 30.
Therefore, in the mobile communication system 100, the user data can be transmitted or received, without being passed through the MSC 60 outside the radio access network 50.
Usually, the MSC 60 is often installed at a site away from the NodeB 20a, 20b to integrate the functions therein, whereas in the mobile communication system 100, the user data can be transmitted or received in the place near the NodeB 20a, 20b, because the MSC 60 is not passed through. Hence, in the mobile communication system 100, the path of user data is shortened as shown in FIG. 14. As a result, in the mobile communication system 100, the line charge can be reduced by the amount of a path via the MSC 60, and a delay on the path can be shortened. Also, several lines, required for all the user data to pass through such redundant paths including the MSC 60, are no longer needed.
Hence, in the mobile communication system 100, the extension transmission or reception and the transmission or reception via the MSC 60, or the extension transmitting/receiving server device 30 for use may be selectively used in a flexible manner in accordance with the situation of the mobile communication system 100 in transmitting or receiving the user data. Therefore, in the mobile communication system 100, it is possible to flexibly deal with a fault occurring in the extension transmitting/receiving server, for example.
Patent Document 1: JP No. 2004-364054 A
Non-Patent Document 1: “Wireless Broadband Textbook”, supervised by Takeshi Hattori and Masanobu Fujioka, IDG Japan, Co. Ltd., Jun. 10, 2002, p. 26 to 37